This is a good point, but to play devil's advocate, the amount of practice time in the NBA is far, far less than in the NCAA. In college, team's are holding practices every day. They're developing skills, working on technical foundations, etc. In the NBA, players are essentially given game time to develop their skills. The very limited amount of practice time is generally used to run sets and go over schemes.

But to counter, the NBA season is longer, teams are more involved in everything (diet, etc) and the NBA resources are generally un-matched by college programs. An NBA team can invest an assistant to spend an entire year with a young player, plust vet mentors, while college can't.